There are many applications in which it is desired to position one or more members with respect to a base or other mounting structure, wherein the member or members can be positioned only in a predetermined way. For example, a device would be useful in teaching wherein plates or cards with letters or numbers thereon can be positioned on a mounting board only in predetermined positions to indicate a correct sequence of letters or numbers, as to spell a word. Although such devices have been proposed, they have been relatively complex and expensive to produce. Further, the known devices have not been easy for a young child to use.
Another application in which it is desired to mount a member with respect to a base or chassis is in electrical devices which use circuits provided on insulating boards wherein each board is to be positioned in a particular place. Various coding arrangements have been used, but have not been entirely satisfactory in identifying the various boards and the positions in which they are to be used.